The present invention relates to an internal combustion engine, and more specifically to an engine control system and process for controlling fuel injection of an engine of a type having a stratified charge combustion mode and a homogeneous charge combustion mode.
Recently, the technique of in-cylinder direct fuel injection in a spark ignition engine such as a gasoline engine is under development to improve the fuel efficiency and emission performance by using stratified charge combustion and homogeneous charge combustion.
In low and medium load regions, a control system for such a type operates an engine in a stratified combustion mode by injecting fuel directly into a combustion chamber during the compression stroke so as to produce a stratified combustible mixture only around the spark plug. The thus-achieved stratified combustion enables stable combustion with an ultra lean mixture, and hence significant improvement in the fuel efficiency and emission performance of the engine.
In a high load region over a predetermined engine load, the engine is operated in a homogeneous combustion mode to meet a demand for higher output torque. In the homogeneous combustion mode, fuel is injected during the intake stroke so as to produce a homogeneous air fuel mixture. (In some examples, a fuel injection valve for the homogeneous mode is provided separately in an intake port.)
The control system changes over the combustion mode between the homogeneous mode and the stratified mode in accordance with one or more engine operating conditions.
An engine control system as disclosed in Japanese Patent Provisional (Kokai) Publication No. 63(1988)-138118 is arranged to always calculate both the fuel injection quantity and injection timing according to the stratified combustion mode and the fuel injection quantity and injection timing according to the homogeneous combustion mode.